Orders not executed with paper trading

Alpaca Trading
1

I’ve noticed my paper account orders will not be executed in the following scenario:
current best bid: x
current best ask: x + 1
submitting a limit buy order for x + 0.5.

I can my x + 0.5 being better than the best bid for a few seconds, other trades happening in the (x, x + 1) range, but my order is still not executed. Is that expected?

In the paper account docs I see: “Orders are filled only when they become marketable. This means that a non-marketable buy limit order will not be filled until its limit price is equal to or greater than the best ask price”. Does that mean the paper account does not match my limit order with market orders?

2

Paper trading tries to simulate live trading but there are limitations. Paper trading executes marketable buy orders at the last ask (offer) and sell orders at the last bid. A limit order doesn’t fill if it is better than those prices. In live trading one can often get ‘price improvement’ so the orders above could often fill. However, the fill prices simulated in paper trading don’t account for any ‘improvement’.